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D. Raja Manohar

Bio: D. Raja Manohar is an academic researcher from Indian Space Research Organisation. The author has contributed to research in topics: Injector & Stagnation temperature. The author has an hindex of 3, co-authored 6 publications receiving 51 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the performance of a second-throat ejector diffuser system employed in high-altitude testing of large-area-ratio rocket motors is considered under various steady and transient operating conditions.
Abstract: The performance of a second-throat ejector―diffuser system employed in high-altitude testing of large-area-ratio rocket motors is considered under various steady and transient operating conditions. When the diffuser attains started condition, supersonic flow fills the entire inlet section and a series of oblique shock cells occurring in the diffuser duct seal the vacuum environment of the test chamber against backflow. The most sensitive parameter that influences the stagnation pressure needed for diffuser starting is the second-throat diameter. Between the throat and exit diameters of the nozzle, there exists a second-throat diameter value that corresponds to the lowest stagnation pressure for starting. When large radial/axial gaps exist between the nozzle exit and diffuser duct, significant reverse flow occurs for the unstarted cases, which spoils the vacuum in the test chamber. However, the starting stagnation- pressure value remains unaffected by the axial/radial gap. Numerical simulations establish that it is possible to arrive at an optimum diffuser geometry that facilitates early functioning of the high-altitude-test facility during motor ignition phase. The predicted axial variations of static pressure and temperature along the diffuser for the testing of a cryogenic upper-stage motor agree well with available experimental data.

24 citations

Journal ArticleDOI
TL;DR: In this article, a second throat ejector using nitrogen as the primary fluid is considered for the creation of a low vacuum in a high-altitude testing facility for large-area-ratio rocket motors.
Abstract: DOI: 10.2514/1.39219 In the present work, a second throat ejector using nitrogen as the primary fluid is considered for the creation of a low vacuum in a high-altitude testing facility for large-area-ratio rocket motors. Detailed numerical investigations have been carried out to evaluate the performance of the ejector for various operational conditions and geometric parametersduring thenonpumpingandpumpingmodesof operation.Inthenonpumpingmode,the lowestvacuum chamberpressureisattainedwhentheprimaryjetjustexpandsuptothemixerthroatandtheresultingsingleshock cellsealsthethroatagainstanybackflow.Thestudyillustrateshoweachgeometricandoperationalparameterofthe ejector can be optimized to meet the test requirements in a high-altitude testing facility byensuring that the primary jet completely expands without a strong impact on the duct wall. When the rocket motor is fully started, due to the self-pumping action, the required vacuum is almost maintained by the exhaust flow itself and the external nitrogen ejector plays only a supplementary role. Numerical predictions for both nonpumping and pumping modes of operation have been validated with experimental data obtained from a scaled-down model of a high-altitude testing facility.

23 citations

Journal ArticleDOI
TL;DR: In this article, the performance characteristics of a high altitude test facility for testing large area ratio rocket engines have been investigated, and the predicted results show that the desired vacuum level is attained when the primary jet flow attaches to the ejector duct walls smoothly, thereby arresting any back flow.
Abstract: In the present study, performance characteristics of a high altitude test facility for testing large area ratio rocket engines have been investigated. Steady-state numerical simulations have been performed initially to highlight the effects of operational parameters on a high altitude test facility operation. Later, the performance of the test facility during the startup phase of the rocket motor has been analyzed. The predicted results show that during the initial high altitude test facility evacuation, the desired vacuum level is attained when the primary jet flow attaches to the ejector duct walls smoothly, thereby arresting any back flow. However, at the fully started condition of the motor, the self-ejector action of the rocket plume plays a major role in maintaining the desired vacuum condition and, hence, the ejector flow rate can be reduced significantly. The injection of water as a fine spray cools the hot gas to a sufficiently low temperature (∼600 K) prior to its release into the atmosphere. T...

6 citations

Journal ArticleDOI
TL;DR: In this paper, the performance of a two-stage external ejector during high-altitude testing of large-area-ratio satellite thrusters is numerically investigated, and the predicted results compare well with in-house experimental data.
Abstract: The performance of a two-stage ejector during high-altitude testing of large-area-ratio satellite thrusters is numerically investigated. Since theflowrate of the exhaust from the satellite thruster is very low, self-ejector action of the exhaust is quite weak; therefore, a two-stage external ejector is required to create the desired low vacuum in the test chamber. The present work attempts to investigate the effects of various operational and geometric parameters on the performance of the two-stage ejector. Predicted results show that the downstream ejector (E2) operation is more critical for maintaining the required vacuum. However, for optimal performance, it is possible to tune the parameters such that both ejectors deliver the same suction effect.Maximumperformance of each ejector is obtained when the primary jet expanding from the nozzle smoothly seals the mixer throat against backflow. Employing a low molecular weight fluid and high stagnation temperature helps in reducing the quantity of fluid required for test facility evacuation. Useful correlations have been derived to quantify the suction performance of the two-stage ejector, and the predicted results compare well with in-house experimental data.

4 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors investigate the secondary flow characteristics and the associated vacuum generation caused with an increase in the primary pressure ramping in zero-secondary flow ejectors, and they find that with the jet expansion reaching a critical level, the fluid supply from the reverse flow is suddenly entrained back into the main jet at the maximum jet expansion point.
Abstract: This paper aims to investigate the secondary flow characteristics and the associated vacuum generation caused with increase in the primary pressure ramping in zero-secondary flow ejectors. The sudden expansion of the primary jet into the diffuser during the ejector start-up results in flow separation from the shear layer formed between the primary and inducted flows and produces large recirculation bubbles in the top and bottom sides of the jet. These recirculation bubbles cause an induced flow from ambient air into the diffuser duct as well. The fluid supply from the reverse flow due to the shear layer separation and the induced flow from ambient air provide a counter momentum against fluid entrainment from a vacuum chamber. As a result of this, the initial vacuum generation process progresses in a slow rate. Thereafter, the primary jet expansion reaches a critical level and a rapid vacuum generation can be seen. It is found that with the jet expansion reaching a critical level, the fluid supply from the reverse flow is suddenly entrained back into the main jet at the maximum jet expansion point. This suddenly reduces the counter-momentum which has been prohibiting the entrainment of fluid from the vacuum chamber and results in rapid evacuation. This is followed by a stage in which the vacuum chamber pressure is increasing due to the attainment of a constant Mach number at the diffuser inlet and the jet pressure ramping. It is found that the secondary flow dynamics and the vacuum generation processes in rectangular and round ejectors show a close resemblance.

24 citations

Journal ArticleDOI
TL;DR: In this paper, the performance of a second-throat ejector diffuser system employed in high-altitude testing of large-area-ratio rocket motors is considered under various steady and transient operating conditions.
Abstract: The performance of a second-throat ejector―diffuser system employed in high-altitude testing of large-area-ratio rocket motors is considered under various steady and transient operating conditions. When the diffuser attains started condition, supersonic flow fills the entire inlet section and a series of oblique shock cells occurring in the diffuser duct seal the vacuum environment of the test chamber against backflow. The most sensitive parameter that influences the stagnation pressure needed for diffuser starting is the second-throat diameter. Between the throat and exit diameters of the nozzle, there exists a second-throat diameter value that corresponds to the lowest stagnation pressure for starting. When large radial/axial gaps exist between the nozzle exit and diffuser duct, significant reverse flow occurs for the unstarted cases, which spoils the vacuum in the test chamber. However, the starting stagnation- pressure value remains unaffected by the axial/radial gap. Numerical simulations establish that it is possible to arrive at an optimum diffuser geometry that facilitates early functioning of the high-altitude-test facility during motor ignition phase. The predicted axial variations of static pressure and temperature along the diffuser for the testing of a cryogenic upper-stage motor agree well with available experimental data.

24 citations

Journal ArticleDOI
TL;DR: In this article, a second throat ejector using nitrogen as the primary fluid is considered for the creation of a low vacuum in a high-altitude testing facility for large-area-ratio rocket motors.
Abstract: DOI: 10.2514/1.39219 In the present work, a second throat ejector using nitrogen as the primary fluid is considered for the creation of a low vacuum in a high-altitude testing facility for large-area-ratio rocket motors. Detailed numerical investigations have been carried out to evaluate the performance of the ejector for various operational conditions and geometric parametersduring thenonpumpingandpumpingmodesof operation.Inthenonpumpingmode,the lowestvacuum chamberpressureisattainedwhentheprimaryjetjustexpandsuptothemixerthroatandtheresultingsingleshock cellsealsthethroatagainstanybackflow.Thestudyillustrateshoweachgeometricandoperationalparameterofthe ejector can be optimized to meet the test requirements in a high-altitude testing facility byensuring that the primary jet completely expands without a strong impact on the duct wall. When the rocket motor is fully started, due to the self-pumping action, the required vacuum is almost maintained by the exhaust flow itself and the external nitrogen ejector plays only a supplementary role. Numerical predictions for both nonpumping and pumping modes of operation have been validated with experimental data obtained from a scaled-down model of a high-altitude testing facility.

23 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the shock transformation in an underexpanded jet in a confined duct when the jet total pressure is increased, and they found that the Mach reflection in the fully undereexpanded jet transforms to a regular reflection (RR) at a certain pressure.
Abstract: This study investigates the shock transformation in an underexpanded jet in a confined duct when the jet total pressure is increased. Experimental study reveals that the Mach reflection (MR) in the fully underexpanded jet transforms to a regular reflection (RR) at a certain jet total pressure. It is observed that neither the incident shock angle nor the upstream Mach number varies during the MR–RR shock transformation. This is in contradiction to the classical MR–RR transformations in internal flow over wedges and in underexpanded open jets. This transformation is found to be a total pressure variation induced transformation, which is a new kind of shock transformation. The present study also reveals that the critical jet total pressures for MR–RR and RR–MR transformations are not the same when the primary pressure is increasing and decreasing, suggesting a hysteresis in the shock transformations.

15 citations

Journal ArticleDOI
TL;DR: In this paper, an experimental study has been carried out to investigate the nature of transients in vacuum ejector flows during start-up and the dynamics in flow characteristics, and the results show that the secondary stream induction progresses with non-uniform rates with the ramping primary jet pressure during startup.
Abstract: An experimental study has been carried out to investigate the nature of transients in vacuum ejector flows during start-up and the dynamics in flow characteristics. The results show that the secondary stream induction progresses with non-uniform rates with the ramping primary jet pressure during start-up. The initial evacuation period is subjected to gradual and highly perturbed secondary fluid entrainment. In this phase, the secondary stream induction by the shear layer is asymmetric leading to an un-even vacuum generation in the secondary chamber. In the second phase, the secondary pressure fluctuations are found to be ceased for a critical primary jet pressure followed by a rapid induction of the secondary fluid till the primary jet expands to the diffuser wall. The transition from the first phase to the second phase is caused by the secondary stream flow choking in the diffuser. Following the second phase, a stable stage exists in the third phase in which the vacuum pressure decreases only marginally. Any further attempt to increase the secondary chamber vacuum level beyond the third phase, by increasing the primary jet total pressure, results in flow reversal into the secondary chamber, spoiling the already achieved vacuum level. In the fourth phase of start-up, a complicated shock interaction transformation from a Mach reflection (MR) to regular reflection (RR) occurs within the diffuser. It is also observed that the primary jet pressures for the minimum secondary chamber pressure, the minimum secondary pressure, and the primary pressure for MR-RR transformation decrease initially with increase in diffuser length and then increase. It is found that the decreasing and increasing trends are caused by the pressure recovery and Fanno effects, respectively.

13 citations